How to sort a map by value in JavaScript?

Question

const myMap = new Map();
myMap.set("a",3);
myMap.set("c",4);
myMap.set("b",1);
myMap.set("d",2);

// sort by value
const mapSort1 = new Map([...myMap.entries()].sort((a, b) => b[1] - a[1]));
console.log(mapSort1);
// Map(4) {"c" => 4, "a" => 3, "d" => 2, "b" => 1}

const mapSort2 = new Map([...myMap.entries()].sort((a, b) => a[1] - b[1]));
console.log(mapSort2);
// Map(4) {"b" => 1, "d" => 2, "a" => 3, "c" => 4}

// sort by key
const mapSort3 = new Map([...myMap.entries()].sort());
console.log(mapSort3);
// Map(4) {"a" => 3, "b" => 1, "c" => 4, "d" => 2}

const mapSort4 = new Map([...myMap.entries()].reverse());
console.log(mapSort4);
// Map(4) {"d" => 2, "b" => 1, "c" => 4, "a" => 3}

Yo could take a different approach and change Symbol.iterator of Map.prototype[@@iterator]() for a custom sorted result.

var map = new Map();

map.set("orange", 10);
map.set("apple", 5);
map.set("banana", 20);
map.set("cherry", 13);

map[Symbol.iterator] = function* () {
    yield* [...this.entries()].sort((a, b) => a[1] - b[1]);
}

for (let [key, value] of map) {     // get data sorted
    console.log(key + ' ' + value);
}

console.log([...map]);              // sorted order
console.log([...map.entries()]);    // original insertation order

.as-console-wrapper { max-height: 100% !important; top: 0; }

In ES6 you can do it like this: (assume your Map object is m).

[...m].map(e =>{ return e[1];}).slice().sort(function(a, b) {
  return a - b; 
});

the spread operator turns a Map object into an array, then takes out the second element of each subarray to build a new array, then sort it. If you want to sort in descending order just replace a - b with b - a.

You can shorten the function and use this in ES6- using arrow function (lambda)

 let m2= new Map([...m.entries()].sort((a,b) => b[1] - a[1]))

You can use list maps instead of map only. Try this:

var yourListMaps = [];
var a = {quantity: 10, otherAttr: 'tmp1'};
var b = {quantity: 20, otherAttr: 'tmp2'};
var c = {quantity: 30, otherAttr: 'tmp3'};
yourListMaps.push(a);
yourListMaps.push(b);
yourListMaps.push(c);

And if you want to sort by quantity, you can:

// Sort c > b > a
yourListMaps.sort(function(a,b){
    return b.quantity - a.quantity;
});

or

// Sort a > b > c
yourListMaps.sort(function(a,b){
    return a.quantity - b.quantity;
});

To sort a map object use the below code.

const map = new Map();
map.set("key","value");
map.set("key","value");

const object = Object.keys(map.sort().reduce((a,b) => (a[k] = map[a], b), {});

console.log(object);

//This will work to sort a map by key.